My fuel tanks have 50mm straight filler spigots (without the normal beading) and I am finding them a bugger to make a good seal to the filler hose with jubilee clips.

Bearing in mind that welding on a bead is not an option, what can I do to improve the seal?

You could try making an epoxy resin bead.

Just work soem resin into some thin string and take a couple of turns around the tube.

I have used these type they work a treat.
Steve,
RS number 526-5549

[Edited on 28/1/07 by stevec]

Mark - The fillers are in an awkward position so access would be tricky to say the least. Nice idea though

Steve - Coincidentally I have just found these myself on eBay. All stainless and less than £3 each too!
eBay